The quality of parts and components used in design: this luxury brand use high quality parts in designing their cars. The interior design, engine, wheels and other parts of their cars are always top notch.
Use of latest technology: Mercedes is one of the first brands to introduce new innovations and technologies to the automobile industry, this shows that a lot of money is put into research and development of technology. The only way to make the money back is by adding this expenses to the cost on each vehicle.
Mercedes is a luxury brand and it has become a household name. To own anything that is luxury, you have to pay the price.
Mercedes make limited version of a particular model, they take special order for a customized version. All these come at a price and that is why Mercedes is expensive.